Fundamental Principles of generators

INTRODUCTION

Depending on the type of aircraft, and the extent to which electrical power is to be utilized for the operation of its systems and components, the primary supply of such power may either be direct current (A.C) or alternating current (A.C)

PRINCIPLE

A generator is a machine that converts mechanical energy into electrical energy by the process of electromagnetic induction.

In both d.c. and a.c. types of generator, the voltage Induced is alternating.

DIFFERENCE BETWEEN AC & DC GENERATOR

The major difference between them being in the method by which the electrical energy is collected and applied

to the circuit externally connected to the generator.

To convert the a.c. produced into unidirectional or d.c., it is necessary to replace the slip rings by a

collecting device, referred to as a commutator.

GENERATOR LOOP CONSTRUCTION

It consists of two segments insulated from each other and connected to the ends of the loop. The brushes are set so that each segment moves out of contact with one brush and into contact with the other at the point where the loop passes through the positions at which induced voltage is minimum.

In other words, a pulsating current increasing to maximum in one direction only is produced.

Effect on output using several coils

In order to smooth out the pulsations and to produce a more constant output, additional wire loops and commutator segments are provided. They are so interconnected and spaced about the axis of rotation, that several are always in a position of maximum action, and the pulsating output is reduced to a ripple.

GENERATOR CLASSIFICATIONS

Generators are classified according to the method by which their magnetic circuits are energized, and the

following tluee classes are normally recognized:

1. Permanent Magnet Generators

2. self excited Generators: electromagnets are excited by current produced by the machines themselves.

3. Separately excited generators: magnets are excited by current obtained from a separate source of d.c

In aircraft d.c. power supply systems, self-excited shunt-wound generators are employed.